A rat monoclonal antibody 4D7 produced by a hybridoma established from a yolk-sac tumor-bearing rat binds selectively to the stage-specific embryonic antigen SSEA-1.

A monoclonal rat IgM (kappa) antibody (MAb) is produced by a hybridoma obtained by fusion of the rat myeloma Y3 Ag 1.2.3 with spleen cells from a female W/Fu rat bearing a yolk-sac carcinoma isograft. In the rat this antibody (4D7) shows strong selective binding to all tested yolk-sac carcinomas, but no binding to cultured cells of a number of other tumor types or to cells of normal tissues. Immunohistochemical analysis of the specificity of the antibody confirmed the strong binding to yolk-sac carcinomas and also revealed binding to some other rat tissues. These include one colon carcinoma, the embryonic ectoderm and the primitive visceral endoderm of 8.5-day-old embryos, the central nervous system and the oviduct epithelium and some cells in the seminal tubules, the gastrointestinal epithelium and associated mucus and also the distal tubuli and collecting ducts of the kidney. The MAb binds strongly to purified SSEA-1 but not to purified Lewis A glycolipid. It is concluded that the 4D7 MAb recognizes a determinant which is identical to or includes Gal beta 1-4(Fuc alpha 1-3) GlcNAc. The immunogenicity of the SSEA-1 determinant is further confirmed by the demonstration that antibodies binding to purified SSEA-1 but not to Lewis A appear in the sera of some of the rats developing primary yolk-sac carcinoma.